Heat Resistant Polyimide Film and Preparation Method Thereof

ABSTRACT

A high temperature resistant polyimide film and its preparation method. The present invention relates to a polyimide film and its preparation method and solves the problems of honeycomb&#39;s and skin panel&#39;s core adhesive—polyimide film with insufficient heat resistance, no climbing of bonding core structure and adhesive fillet formation. The high temperature resistant polyimide film is made by polyimide solution, inorganic filler modifier and interface coupling agent by the steps of: under specific temperature and stirring conditions, adding inorganic filler modifier and interface coupling agent to polyimide solution, stirring to obtain the adhesive agent; filtering and degassing the adhesive agent, casting to a stainless steel drum with carrier cloth and release paper to obtain a self-supporting film; then heating and annealing to obtain the final polyimide film. The present invention is applied to high temperature resistant polyimide film and its preparation method.

BACKGROUND OF THE PRESENT INVENTION Field of Invention

The present invention relates to polyimide film and its preparationmethod thereof.

Description of Related Arts

With the technological development of research and application inaviation and aerospace industries, the Mach number of high-speedaircraft has increased year by year, requiring a lightweight structureof honeycomb-wall panel (panel-core) sandwich structure at 300° C. andabove, especially at 400° C.˜500° C. with relatively good mechanicalproperties and thermal stability. The use of aluminum honeycomb, NOMEXhoneycomb, KEVLAR honeycomb and etc. fails to meet the honeycombtemperature requirements of above 300° C. The use of polyimide honeycomb(such as HRH327 from HEXCEL corporation) and titanium alloy honeycombcan meet the temperature resistance requirements of honeycomb, and theweight loss effect of titanium alloy honeycomb is not as good aspolyimide honeycomb while the polyimide honeycomb requires lower curingpressure in the curing process. This type of material is in urgent needin the manufacture of aerospace equipment. In the manufacturing processof honeycomb sandwich structure, the quality of the panel and itsbonding strength with the honeycomb core are the key factors affectingthe performance of the sandwich structure. Therefore, the selection ofbonding adhesive is crucial.

In general, the adhesive can be classified into different forms such asa solution, a paste, and a film. Among them, the core film has theadvantages of uniform thickness, accurate glue dosage, simpleconstruction process, and applicable for use in large-area bonding, andis the first choice for bonding honeycomb sandwich structure. Among theexisting high temperature resistant adhesive films, the modified epoxyfilm, the cyanate film and the double horse film are widely used, butthe use temperature generally does not exceed 300° C. As the usetemperature of the structure increases, higher, the heat resistancerequirements of the film increases. In order to achieve a highertemperature resistance grading, the polyimide core film with superiorheat resistance and high temperature bonding properties becomes aninevitable choice. However, adhesives for bonding lightweight andhigh-strength polyimide honeycomb and composite panels need to meet thefollowing additional requirements:

First, it is necessary to meet the low pressure curing of the honeycomb(≤0.5 MPa) to avoid honeycomb cell collapse caused by high pressurecuring, which in turn affecting the structural quality. This requires apolyimide film with better melt flow and lower melt viscosity under hightemperature condition;

Second, after the honeycomb-core structure is cured, the adhesive needsto have a certain degree of climbing ability at the bottom end of thehoneycomb in order to have a relatively higher core peel strength tomeet the process requirements. The above phenomenon can be achieved bycapillary action, melt flowability and thixotropy. The polyimideadhesive cured with honeycomb-skin needs to be able to realize thefilm-forming property of the core film and the formation of the fillethas a great contribution to the stability of the core structure.

Third, the core film needs to meet the temperature resistancerequirements of honeycomb and composite materials, that is, the userequirements of above 300° C., and especially 400° C.˜500° C. That is,high shear strength, flatwise tensile strength and peel strengthrequirements at high temperatures.

The existing polyimide adhesives are classified into two types, whichare polycondensation type and addition type. The LARC-TPI developed bythe Langley Research Center of NASA in the United States in 1980 is atypical polycondensation polyimide film (Polym. Inter, 1996; 41:193-207). Its Tg is about 260° C., it has no weight loss phenomenonbefore 400° C. after treatment at 300 C in air, and it has good thermaloxidative stability. After curing, the shear strength of the bondedtitanium alloy at room temperature was 36.5 MPa, and remained at 13.1MPa at 232° C. In order to further reduce the cost of raw materials, theLangley Research Center has developed a series of thermoplasticpolyimide films with different structures (J. Ahes., 1988; 30:185-198.), with a monomer structure such as p-phenylenediamine,m-phenylenediamine and diphenyl ether diamine, which also achieve goodbonding properties. Progar (J. Adhes. Adhes., 1984; 4: 79-86.) et al.used BTDA and 3,3-DDS to synthesize a polyimide film PISO₂ containing asulfone group structure, which has the thermoplastic of polysulfone andthe thermal resistance of polyimide. Its Tg is 273° C. When bonding withtitanium alloy, its shear strength at room temperature and 232° C. are32.0 and 18.1 MPa respectively. After heat aging at 204° C. for 5000 h,its shear strength at 204° C. is still as high as 20.5 MPa. Maudgal etal. (J. Adhes. Adhes., 1984; 4: 87-90.) utilize siloxane-containing1,3-bis(aminopropyl)tetramethyldisiloxane and 3,3-diaminobenzophenonefor copolymerization with 3,3,4,4-dibenzophenonetetracarboxylicdianhydride (BTDA) together to obtain a AxBy type thermoplasticpolyimide film containing siloxane structure, through which the hightemperature strength of the polyimide and the low temperature propertiesof the siloxane are organically combined. In recent years, LaRC-CPI(Aurum PIXA) (Science of Advanced Materials and Process EngineeringSeries, 1977, 22: 221) has stronger bonding strength for titanium alloybonding at room temperature and high temperature due to the use of moreketone carbonyl and ether linkage monomers, reaching 49.1 MPa and 25.3MPa (232° C.) respectively. However, the Tg value of the above film doesnot exceed 300° C., and it is difficult for the use temperature toexceed 300° C.

The additional type polyimide adhesive is formed by dissolving the imideprepolymer in an organic solvent such as DMAc or DMF as an adhesivethrough controlling the molar ratio and blocking agent of feedingmaterials, and then processing heating and cross-linking curing, and aremainly for bonding at short time period and high temperature resistanceconditions. Moreover, since no volatile substances is released duringcuring, it is suitable for large-area bonding. Since highly crosslinkedstructure is formed after curing, the addition type polyimide adhesivehas excellent heat resistance. However, the toughness of the curedproduct is poor and it is difficult for use to prepare a film with hightoughness requirements. Currently, the common thermosetting polyimidesinclude: (1) NA anhydride (5-norbornene-2,3-dicarboxylic anhydride)end-capped PMR type polyimide; (2) alkynyl terminated polyimide.

The PMR type polyimide is capped with norbornene, the low viscosity ofthe polyamic acid is formed by using the tetracarboxylic acid diester sothat the content is controlled to 50% or more. Cytec's FM35 design has amolecular weight of 1500 g/mol, a cure temperature of 329° C., a curepressure of 0.35 MPa, and a postcure at 343° C. The Ti/Ti shear strengthwas 17.2 MPa (25° C.), 13.8 MPa (288° C.) (12th Nat. SAMPE Tech. Con. f,1980: 746-758). However, after the PMR-type polyimide is subjected tothermal oxidative aging at 316° C. for 125 h, the shear strength islowered rapidly. This is due to the poor long-term thermal oxidativestability of the aliphatic norbornene group, so it does not meet thelong-term bonding requirements of more than 300° C. (or even 400° C. to500° C.).

The alkynyl-terminated polyimide has two types of curing, which areacetylene-based polyimide curing (cured at 250° C.) andphenylethynyl-based polyimide curing (cured at 370° C.). Compared withanhydride-terminated polyimide, its long-term thermal oxidativestability is better. In 1974, Hughes Aircraft Corporation of the UnitedStates introduced HR-600 acetylene-terminated polyimide (Thermid 600),which produced a cured product with a Tg of up to 350° C. and a thermaldecomposition temperature of over 500° C. However, the processing windowis narrow due to its high melting point and the immediate initiation ofpolymerization after melting. For example, ThermidMC-600 has a gel timeof only 3 min at 190° C., so this series of resins as an adhesive doesnot form a good wetting effect on the surface to be bonded (4th Nat.SAMPE Tech. Con. f. 1982: 236-242).

Since ethynyl-terminated polyimides generally have the disadvantage ofnarrow processing window, phenylethynyl-terminated polyimide prepolymerswere developed in the 1980s. Compared with ethynyl groups,phenylethynyl-terminated prepolymers have better chemical stability andthermal stability, and their imide prepolymers have better fluidity anda wider processing window. Since the melting time of the resin beforethe reaction is long, the wettability of the adherend is increased.PETI-5 (molecular weight: 5000 g/mol) has the best shear strength (52MPa, 25° C.; 34 MPa, 177° C.) (Polym. Prep. 1994, 35: 553). However, theabove polycondensation type and addition type polyimide adhesivesgenerally have the following problems in the application of a corestructure (composite-honeycomb sandwich structure):

First, in order to meet the low pressure curing of honeycomb (≤0.5 MPa),a structure that can be thermally melted is required. If it is apolycondensation type polyimide, it is thermoformed at 400° C. or below(Tm (melting point) or Tg (glass transition temperature) <400° C.), andthe use temperature does not exceed 400° C. As reported in the aboveliteratures, the use temperature is not more than 400° C. The use ofaddition type polyimide can meet low processing viscosity, which resultsin small molecular weight and great brittleness of cured material. Forthe core structure, this will cause the structural member to face theproblem of subsequent damages such as cutting, bending and the like. Atthe same time, in conventional addition type polyimide film, nothing inthe reports and literatures can satisfy the Tg value above 400° C., theuse temperature above 400° C., and the bonding requirements of the coresandwich structure.

After the honeycomb-core structure is cured, the adhesive needs to havea certain degree of climbing ability at the bottom end of the honeycombin order to have a relatively higher core peel strength to meet theprocess requirements. The above phenomenon can be achieved by capillaryaction, melt flowability and thixotropy. The polyimide adhesive curedwith honeycomb-skin needs to be able to realize the film-formingproperty of the core film and the formation of the fillet has a greatcontribution to the stability of the core structure. However, ingeneral, the formation of a climbable fillet requires the adhesive tohave a suitable viscosity and bonding ability. Reports or disclosures inrelation to the control of the climbing ability and the fillet in thecore film to obtain a good bonding effect is not found.

The existing data and literature reports focus on the structural designof the addition type and polycondensation type polyimides, and very fewreports focus on the shear strength, flatwise tensile strength and peelstrength at high temperatures of the adhesive used in the structure. Noreports on plate-core bonded polyimide film with high temperatureresistance (400° C. to 500° C.) can be found. There is also no datareport on how to meet the high temperature resistance, high bondtoughness and interface bonding effect at the same time.

SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to solve the existing problems ofcore adhesive in honeycomb and skin panels—polyimide film, which hasinsufficient thermal resistance, and no climbing and formation ofadhesive fillet in core structure bonding, and to provide a hightemperature resistant polyimide film and its method of manufacturethereof.

A high temperature resistant polyimide film, which is manufactured by:100 parts by weight of polyimide solution; 10 parts to 40 parts byweight of inorganic filler modifier; and 0.1 parts by weight˜5 partsinterface coupling agent,

wherein the inorganic filler modifier consists of silicon dioxide(silica)-based substance and substance for increasing interface bonding,and the mass ratio of the silica-based substance and the substance forincreasing interface bonding is 1:(0.1˜0.5),

the silica-based substance is hollow ceramic microspheres, fumed silica(silicon dioxide in gaseous state), fused silica (melted silicondioxide) or amorphous silica;

the substance for increasing interface bonding is one or a mixture oftwo of: aluminum hydroxide, magnesium hydroxide, molybdenum oxide,aluminum nitride, aluminum oxide, boron nitride and silicon carbide;

the polyimide solution comprises polyimide which has a structuralformula of:

where n is 1˜19;wherein Ar₁ has a structural formula of:

wherein Ar₂ has a structural formula of:

where R₁ is O or NH.

A method of preparing high temperature resistant polyimide film, whichcomprises the following steps:

(1) weighing to obtain 100 parts of polyimide solution, 10 parts to 40parts of inorganic filler modifier and 0.1 part to 5 parts of interfacecoupling agent; adding 10 to 40 parts of inorganic filler modifier and0.1 part to 5 parts of interface coupling agent to 100 parts ofpolyimide solution under a temperature of 90° C. to 120° C. and stirringconditions; and stirring for 10 minutes to 30 minutes to obtain anadhesive agent;

wherein the polyimide solution is manufactured by a process comprisingthe steps of: adding N,N-dimethylacetamide in a three-neck flask; addingaromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 hour to 5 hours; then adding aromaticdianhydride to the three-neck flask and stirring for 1 hour to 5 hoursto obtain a mixed solution; adding 4-phenylethynylphthalic anhydride tothe mixed solution, stirring and allowing reaction for 1 hour to 5hours; then adding toluene, heating to a temperature of 120° C. to 130°C. and carrying out reflux reaction for 5 hours to 20 hours under atemperature condition of 120° C.˜130° C. to obtain the polyimidesolution;

wherein a molar ratio of aromatic dianhydride to aromatic diamine is(0.50˜0.95):1; a mass ratio of N,N-dimethylacetamide to toluene is1:(0.2˜0.5); a molar ratio of aromatic diamine to4-phenylethynylphthalic anhydride is 1:(0.01˜1); and a total number ofmoles of anhydride functional group in the aromatic dianhydride and4-phenylethynyl phthalic anhydride is equal to the number of moles ofamino functional group of the aromatic diamine;

a ratio of a total mass of the N,N-dimethylacetamide and the toluene toa total mass of the 4-phenylethynylphthalic anhydride, the aromaticdianhydride and the aromatic diamine is (2.5˜4):1;

the aromatic anhydride is:

the aromatic diamine has a structural formula of:

where R₁ is O or NH;

(2) filtering and degassing the adhesive agent, casting to a rotatingdrum made of stainless steel and loaded with carrier cloth and releasepaper to obtain a self-supporting film; then under a temperature of 60°C. to 150° C., heating for 1 min to 60 min, then under a temperature of150° C. to 300° C., heating for 1 min to 60 min, and finally under atemperature of 50° C. to 140° C., annealing for 1 min to 20 min toobtain high temperature resistant polyimide film;

wherein the high temperature resistant polyimide film has a thickness of0.30 mm˜0.60 mm;

in the step (1), the inorganic filler modifier consists of silicondioxide (silica)-based substance and substance for increasing interfacebonding, and the mass ratio of the silica-based substance and thesubstance for increasing interface bonding is 1:(0.1˜0.5),

the silica-based substance is hollow ceramic microspheres, fumed silica(silicon dioxide in gaseous state), fused silica (melted silicondioxide) or amorphous silica,

the substance for increasing interface bonding is one or a mixture oftwo or more selected from the group consisting of: aluminum hydroxide,magnesium hydroxide, molybdenum oxide, aluminum nitride, aluminum oxide,boron nitride and silicon carbide;

in the step (1), the polyimide solution comprises polyimide which has astructural formula of:

where n is 1˜19;where Ar₁ has a structural formula of:

where Ar₂ has a structural formula of:

where R₁ is O or NH.

The present invention has the following advantageous effects:

The conventional core (honeycomb-composite materials) structure withpolyimide film fails to meet the temperature resistance requirements of300° C. or above, and especially of 400° C.˜500° C., and therefore failsto meet the interface bonding requirements of new structure. At the sametime, less reports are focused on climbing ability (fillet) formation,the shear strength, flatwise tensile strength and peel strength at highand low temperatures, which are required for high toughness, of theconventional polyimide film.

The present invention employs an aromatic diamine containing a nitrogenheterocyclic structure and polymerizes with an aromatic dianhydride toform a polyimide, which has a higher material modulus and rigidity whencompared with biamine with an ordinary benzene ring structure as in theinformation and the literature. Also, the introduction of thebenzimidazole or benzoxazole structure forms another coplanar rod-likestructure other than the benzimidazole ring, which improves the glasstransition temperature and heat resistance. Unexpectedly, above Tgvalue, due to the retention of the rigid structure, it still has a veryhigh modulus value, and the modulus drops is within a 0.5 order ofmagnitude, so it has a performance of more than Tg, so that it cansatisfy the use requirements of 400° C.˜500° C. In addition, theintroduction of a flexible group in the aromatic diamine is avoided sothat it is ensured that each repeating unit from the imide ring to thebenzimidazole and to the imide ring has a rigid linear structure to forma rigid segment, which further improve the strength performance at hightemperature of the overall structure. In addition, the use of a diaminewith a symmetrical structure can further enhance the structural order ofthe material and obtain better high temperature strength.

Second, the following aromatic dianhydride groups:

which contain a rotatable angle or steric hindranceare, are selected,and rigid coplanar structures including pyromellitic dianhydride are notused. Therefore, on the one hand, it can improve the flexibility of thesegment and provide a certain degree of melt processibility throughcontrolling the molecular weight by adjusting the number of repeatingunits; on the other hand, by introducing C═O, S═O, CF, and etc., whichcan form chemical bonding with surface groups of heterogeneous materialssuch as hydroxyl groups, carboxyl groups, etc., the interface bondingperformance is increased, the shear strength and toughness is improved,and especially the heat resistance is improved while the peel strengthis increased significantly.

It is difficult to obtain good film-forming property by usingthermosetting resin alone. The carrier cloth is proposed to achieveself-supporting property of the film being formed. In addition, the useof non-polar filler can better achieve film forming toughness and highsurface quality, reduce crack generation and improve product thicknessuniformity. Among which, through experiments, it is found that a bettereffect is obtained by using silica-based materials.

It is difficult to form a good interfacial bonding effect by the thermalmelting behavior of the thermosetting polyimide resin alone: a resinwith a low melt viscosity, which has a good fluidity, has no climbingability at the bottom end of the honeycomb, and cannot providing abonding effect; a resin with high melt viscosity, which has poorfluidity, cannot form a capillary phenomenon at the bottom end of thehoneycomb, and cannot providing a bonding effect.

The present invention employs a flow control agent to control thethixotropic and capillary climbing effects of the resin, thereby forminga desired fillet and obtaining a good bonding effect. Unexpectedly, theuse of a mixture of thixotropy-controlling silica substances for and ansubstance for increasing interface bonding such as oxides, carbides,nitrides can improve the fluidity of the resin melt while the climbingresistance is suppressed, thus resulting the retention of fillet effectafter curing as well as a better peel toughness. When the mass ratio ofthe silica-based substance and the substance for increasing interfacebonding is 1:(0.1˜0.5), the best overall effect is obtained. Moreover,when the mass ratio of the added inorganic filler modifier to thepolyimide solution is (0.1 to 0.4):1, a good core-structure bondingeffect is obtained, which is mainly reflected by proper climbing abilityand fillet formation, that excessive filler will affect the resin meltflow and capillary climbing action at the bottom end of the honeycomband inadequate filler will lead to failure to control thixotropy.

The formula of the invention is reasonable, and the prepared film hasthe thermal resistance above 300° C., and especially has the thermalresistance and the bonding ability of the core structure at 400° C.˜500°C., and an excellent interface bonding effect can be obtained. It can beused for bonding polyimide honeycomb, titanium alloy honeycomb andpolyimide composite materials, titanium alloy and stainless steelstructural parts, which requires relatively higher thermal performance,thus broadening the applications of adhesives with high temperatureresistant in aerospace and aviation industries.

The present invention is applied to a high temperature resistantpolyimide film and its manufacturing method thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an infrared spectrum, 1 is an infrared curve after curing ofthe polyimide solution prepared in synthesis embodiment 1; and 2 is aninfrared curve after curing of the polyimide solution prepared insynthesis embodiment 3.

FIG. 2 is a rheological graph, 1 is a rheological curve of polyimide inthe polyimide solution prepared in synthesis embodiment 1; 2 is arheological curve of polyimide in the polyimide solution prepared insynthesis embodiment 6; and 3 is the rheological curve of polyimide inthe polyimide solution prepared in synthesis embodiment 3.

FIG. 3 is a dynamic thermomechanical curve, 1 is a dynamicthermomechanical curve after curing of the polyimide solution preparedin synthesis embodiment 1; 2 is a dynamic thermomechanical curve aftercuring of the polyimide solution prepared in synthesis embodiment 3; 3is a dynamic thermomechanical curve after curing of the polyimidesolution prepared in synthesis embodiment 5, and 4 is a dynamicthermomechanical curve after curing of the polyimide solution preparedin synthesis embodiment 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Preferred Embodiment 1

According to this embodiment, a high temperature resistant polyimidefilm is manufactured by: 100 parts by weight of polyimide solution; 10parts to 40 parts by weight of inorganic filler modifier; and 0.1parts˜5 parts by weight of interface coupling agent,

wherein the inorganic filler modifier consists of silicon dioxide(silica)-based substance and substance for increasing interface bonding,and the mass ratio of the silica-based substance and the substance forincreasing interface bonding is 1:(0.1˜0.5),

the silica-based substance is hollow ceramic microspheres, fumed silica(silicon dioxide in gaseous state), fused silica (melted silicondioxide) or amorphous silica;

the substance for increasing interface bonding is one or a mixture oftwo or more of: aluminum hydroxide, magnesium hydroxide, molybdenumoxide, aluminum nitride, aluminum oxide, boron nitride and siliconcarbide;

the polyimide solution comprises polyimide which has a structuralformula of:

where n is 1˜19;wherein Ar₁ has a structural formula of:

wherein Ar₂ has a structural formula of:

where R₁ is O or NH.

The structural formula of the polyimide in the polyimide solutioncontains a nitrogen heterocyclic structure. Preferably, the nitrogenheterocyclic structure is bonded to the diamine structure and contains areactive end group, which is terminated with 4-phenylethynyl phthalicanhydride.

The silica-based substance can control thixotropic flow properties.

The advantageous effect of this preferred embodiment is as follows: Theconventional core (honeycomb-composite materials) structure withpolyimide film fails to meet the temperature resistance requirementsabove 300° C., and especially of 400° C.˜500° C., and therefore fails tomeet the interface bonding requirements of new structure. At the sametime, less reports are focused on climbing ability (fillet) formation,the shear strength, flatwise tensile strength and peel strength at highand low temperatures, which are required for high toughness, of theconventional polyimide film.

The present invention employs an aromatic diamine containing a nitrogenheterocyclic structure and polymerizes with an aromatic dianhydride toform a polyimide, which has a higher material modulus and rigidity whencompared with biamine with an ordinary benzene ring structure as in theinformation and the literature. Also, the introduction of thebenzimidazole or benzoxazole structure forms another coplanar rod-likestructure other than the benzimidazole ring, which improves the glasstransition temperature and heat resistance. Unexpectedly, above Tgvalue, due to the retention of the rigid structure, it still has a veryhigh modulus value, and the modulus drops is within a 0.5 order ofmagnitude, so it has a performance of more than Tg, so that it cansatisfy the use requirements of 400° C.˜500° C. In addition, theintroduction of a flexible group in the aromatic diamine is avoided sothat it is ensured that each repeating unit from the imide ring to thebenzimidazole and to the imide ring has a rigid linear structure to forma rigid segment, which further improve the strength performance at hightemperature of the overall structure. In addition, the use of a diaminewith a symmetrical structure can further enhance the structural order ofthe material and obtain better high temperature strength.

Second, in this embodiment, the following aromatic dianhydride groups:

which contain a rotatable angle or steric hindrance are, are selected,and rigid coplanar structures including pyromellitic dianhydride are notused. Therefore, on the one hand, it can improve the flexibility of thesegment and provide a certain degree of melt processibility throughcontrolling the molecular weight by adjusting the number of repeatingunits; on the other hand, by introducing C═O, S═O, CF, and etc., whichcan form chemical bonding with surface groups of heterogeneous materialssuch as hydroxyl groups, carboxyl groups, etc., the interface bondingperformance is increased, the shear strength and toughness is improved,and especially the heat resistance is improved while the peel strengthis increased significantly.

It is difficult to obtain good film-forming property by usingthermosetting resin alone. The carrier cloth is proposed to achieveself-supporting property of the film being formed. In addition, the useof non-polar filler can better achieve film forming toughness and highsurface quality, reduce crack generation and improve product thicknessuniformity. Among which, through experiments, it is found that a bettereffect is obtained by using silica-based materials.

It is difficult to form a good interfacial bonding effect by the thermalmelting behavior of the thermosetting polyimide resin alone: a resinwith a low melt viscosity, which has a good fluidity, has no climbingability at the bottom end of the honeycomb, and cannot providing abonding effect; a resin with high melt viscosity, which has poorfluidity, cannot form a capillary phenomenon at the bottom end of thehoneycomb, and cannot providing a bonding effect.

The present invention employs a flow control agent to control thethixotropic and capillary climbing effects of the resin, thereby forminga desired fillet and obtaining a good bonding effect. Unexpectedly, theuse of a mixture of thixotropy-controlling silica substances for and ansubstance for increasing interface bonding such as oxides, carbides,nitrides can improve the fluidity of the resin melt while the climbingresistance is suppressed, thus resulting the retention of fillet effectafter curing as well as a better peel toughness. When the mass ratio ofthe silica-based substance and the substance for increasing interfacebonding is 1:(0.1˜0.5), the best overall effect is obtained. Moreover,when the mass ratio of the added inorganic filler modifier to thepolyimide solution is (0.1 to 0.4):1, a good core-structure bondingeffect is obtained, which is mainly reflected by proper climbing abilityand fillet formation, that excessive filler will affect the resin meltflow and capillary climbing action at the bottom end of the honeycomband inadequate filler will lead to failure to control thixotropy.

The formula of the invention is reasonable, and the prepared film hasthe thermal resistance above 300° C., and especially has the thermalresistance and the bonding ability of the core structure at 400° C.˜500°C., and an excellent interface bonding effect can be obtained. It can beused for bonding polyimide honeycomb, titanium alloy honeycomb andpolyimide composite materials, titanium alloy and stainless steelstructural parts, which requires relatively higher thermal performance,thus broadening the applications of adhesives with high temperatureresistant in aerospace and aviation industries.

Preferred Embodiment 2

This embodiment differs from Embodiment 1 in that the polyimide solutionis prepared according to the following steps:

adding N,N-dimethylacetamide in a three-neck flask; adding aromaticdiamine to the N,N-dimethylacetamide under a nitrogen atmosphere andstirring for 1 hour to 5 hours; then adding aromatic dianhydride to thethree-neck flask and stirring for 1 hour to 5 hours to obtain a mixedsolution; adding 4-phenylethynylphthalic anhydride to the mixedsolution, stirring and allowing reaction for 1 hour to 5 hours; thenadding toluene, heating to a temperature of 120° C. to 130° C. andcarrying out reflux reaction for 5 hours to 20 hours under a temperaturecondition of 120° C.˜130° C. to obtain the polyimide solution;

wherein a molar ratio of aromatic dianhydride to aromatic diamine is(0.50˜0.95):1; a mass ratio of N,N-dimethylacetamide to toluene is1:(0.2˜0.5); a molar ratio of aromatic diamine to4-phenylethynylphthalic anhydride is 1:(0.01˜1); and a total number ofmoles of anhydride functional group in the aromatic dianhydride and4-phenylethynyl phthalic anhydride is equal to the number of moles ofamino functional group of the aromatic diamine;

a ratio of a total mass of the N,N-dimethylacetamide and the toluene toa total mass of the 4-phenylethynylphthalic anhydride, the aromaticdianhydride and the aromatic diamine is (2.5˜4):1;

the aromatic anhydride is:

the aromatic diamine has a structural formula of:

where R₁ is O or NH. Others are the same as in the Embodiment 1.

Preferred Embodiment 3

This embodiment differs from Embodiment 1 or Embodiment 2 in that: theinorganic filler modifier has an average particle diameter of 0.1 μm to10 μm; the interface coupling agent is a silane coupling agentcontaining amino end group. Others are the same as in the Embodiment 1or Embodiment 2.

The average particle diameter of the inorganic filler modifier needs tomeet the requirement of dispersion uniformity. Preferably, the averageparticle diameter is 0.5 μm˜3 μm.

Preferred Embodiment 4

This embodiment differs from one of the Embodiment 1 to 3 in that: thesilane coupling agent containing amino end group isγ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane or3-aminopropylmethyldiethoxysilane. Others are the same as in theEmbodiments 1-3.

Preferred Embodiment 5

This embodiment provides a method of preparing high temperatureresistant polyimide film with the following steps:

(1) weighing to obtain 100 parts of polyimide solution, 10 parts to 40parts of inorganic filler modifier and 0.1 part to 5 parts of interfacecoupling agent; adding 10 to 40 parts of inorganic filler modifier and0.1 part to 5 parts of interface coupling agent to 100 parts ofpolyimide solution under a temperature of 90° C. to 120° C. and stirringconditions; and stirring for 10 min-30 min to obtain an adhesive agent;

the polyimide solution is manufactured by a process comprising thefollowing steps: adding N,N-dimethylacetamide in a three-neck flask;adding aromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 h˜5 h; then adding aromatic dianhydride tothe three-neck flask and stirring for 1 h˜5 h to obtain a mixedsolution; adding 4-phenylethynylphthalic anhydride to the mixedsolution, stirring and allowing reaction for 1 h˜5 h; then addingtoluene, heating to a temperature of 120° C.˜130° C. and carrying outreflux reaction for 5 h˜20 h under a temperature condition of 120°C.˜130° C. to obtain the polyimide solution;

wherein a molar ratio of aromatic dianhydride to aromatic diamine is(0.50˜0.95):1; a mass ratio of N,N-dimethylacetamide to toluene is1:(0.2˜0.5); a molar ratio of aromatic diamine to4-phenylethynylphthalic anhydride is 1:(0.01˜1); and a total number ofmoles of anhydride functional group in the aromatic dianhydride and4-phenylethynyl phthalic anhydride is equal to the number of moles ofamino functional group of the aromatic diamine;

a ratio of a total mass of the N,N-dimethylacetamide and the toluene toa total mass of the 4-phenylethynylphthalic anhydride, the aromaticdianhydride and the aromatic diamine is (2.5˜4):1;

the aromatic anhydride is:

the aromatic diamine has a structural formula of:

where R₁ is O or NH;

(2) filtering and degassing the adhesive agent, casting to a rotatingdrum made of stainless steel and loaded with carrier cloth and releasepaper to obtain a self-supporting film; then under a temperature of 60°C.˜150° C., heating for 1 min˜60 min, then under a temperature of 150°C.˜300° C., heating for 1 min˜60 min, and finally under a temperature of50° C.˜140° C., annealing for 1 min˜20 min to obtain high temperatureresistant polyimide film;

the high temperature resistant polyimide film has a thickness of 0.30mm˜0.60 mm;

in the step (1), the inorganic filler modifier consists of silicondioxide (silica)-based substance and substance for increasing interfacebonding, and the mass ratio of the silica-based substance and thesubstance for increasing interface bonding is 1:(0.1˜0.5);

the silica-based substance is hollow ceramic microspheres, fumed silica(silicon dioxide in gaseous state), fused silica (melted silicondioxide) or amorphous silica;

the substance for increasing interface bonding is one or a mixture oftwo or more of: aluminum hydroxide, magnesium hydroxide, molybdenumoxide, aluminum nitride, aluminum oxide, boron nitride and siliconcarbide;

in the step (1), the polyimide solution comprises polyimide which has astructural formula of:

where n is 1˜19;where Ar₁ has a structural formula of:

where Ar₂ has a structural formula of:

where R₁ is O or NH.

Preferred Embodiment 6

This embodiment differs from Embodiment 5 in that: in the step (1), theaverage particle diameter of the inorganic filler modifier is 0.1 μm˜10μm. Others are the same as in the Embodiment 5.

Preferred Embodiment 7

This embodiment differs from Embodiment 5 or Embodiment 6 in that: inthe step (1), the interface coupling agent is a silane coupling agentcontaining amino end group. Others are the same as in the Embodiment 5or Embodiment 6.

Preferred Embodiment 8

This embodiment differs from one of the Embodiment 5-7 in that: thesilane coupling agent containing amino end group isγ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane or3-aminopropylmethyldiethoxysilane. Others are the same as in theEmbodiments 5-7.

Preferred Embodiment 9

This embodiment differs from one of the Embodiment 5-8 in that: in thestep (2), the carrier cloth is: E-glass fiberglass cloth, D-glassfiberglass cloth, S-glass fiberglass cloth, NE-glass fiberglass cloth,T-glass fiberglass cloth or Q-glass fiberglass cloth. Others are thesame as in the Embodiments 5-8.

The carrier cloth is a glass carrier cloth, which can be used for knownmaterials for various printed circuit boards and composite materials.Among these substrates, it is more preferable to use E-glass fiberglasscloth which has excellent expansion coefficient in the planar directionand excellent balance in drilling process.

Preferred Embodiment 10

This embodiment differs from one of the Embodiment 5-9 in that: thecarrier cloth has a surface density of 100 g/cm²˜110 g/cm². Others arethe same as in the Embodiments 5-9.

The following embodiments are used to verify the beneficial effects ofthe present invention:

Synthesis Embodiment 1

The polyimide solution is prepared according to the following steps:adding 189 g N,N-dimethylacetamide in a three-neck flask; adding 41.65 g(0.1 mol) aromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 h; then adding 14.71 g (0.05 mol)3,3′,4,4′-biphenyltetracarboxylic dianhydride to the three-neck flaskand stirring for 5 hours to obtain a mixed solution; adding 24.82 g (0.1mol) 4-phenylethynylphthalic anhydride to the mixed solution, stirringand allowing reaction for 3 hours; then adding 62 g toluene, heating toa temperature of 130° C. and carrying out reflux reaction for 10 hoursunder a temperature condition of 130° C. to obtain the polyimidesolution;

the 3,3′,4,4′-biphenyltetracarboxylic dianhydride has a structuralformula of:

the aromatic diamine has a structural formula of:

the CAS number of the aromatic diamine is: 4402-17-9;

the polyimide in the polyimide solution has a structural formula of:

wherein Ar₂ has a structural formula of:

Synthesis Embodiment 2

The polyimide solution is prepared according to the following steps:adding 175 g N,N-dimethylacetamide in a three-neck flask; adding 41.65 g(0.1 mol) aromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 h; then adding 23.54 g (0.08 mol)3,3′,4,4′-biphenyltetracarboxylic dianhydride to the three-neck flaskand stirring for 5 hours to obtain a mixed solution; adding 9.93 g (0.04mol) 4-phenylethynylphthalic anhydride to the mixed solution, stirringand allowing reaction for 3 hours; then adding 58 g toluene, heating toa temperature of 130° C. and carrying out reflux reaction for 10 hoursunder a temperature condition of 130° C. to obtain the polyimidesolution;

the 3,3′,4,4′-biphenyltetracarboxylic dianhydride has a structuralformula of:

the aromatic diamine has a structural formula of:

the CAS number of the aromatic diamine is: 4402-17-9;

the polyimide in the polyimide solution has a structural formula of:

wherein Ar₂ has a structural formula of:

Synthesis Embodiment 3

The polyimide solution is prepared according to the following steps:adding 190 g N,N-dimethylacetamide in a three-neck flask; adding 41.65 g(0.1 mol) aromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 h; then adding 16.11 g (0.05 mol)3,3′,4,4′-benzophenonetetracarboxylic dianhydride to the three-neckflask and stirring for 5 hours to obtain a mixed solution; adding 24.82g (0.1 mol) 4-phenylethynylphthalic anhydride to the mixed solution,stirring and allowing reaction for 3 hours; then adding 63 g toluene,heating to a temperature of 130° C. and carrying out reflux reaction for10 hours under a temperature condition of 130° C. to obtain thepolyimide solution;

the 3,3′,4,4′-benzophenonetetracarboxylic dianhydride has a structuralformula of:

the aromatic diamine has a structural formula of:

the CAS number of the aromatic diamine is: 4402-17-9;

the polyimide in the polyimide solution has a structural formula of:

where Ar₂ has a structural formula of:

Synthesis Embodiment 4

The polyimide solution is prepared according to the following steps:adding 180 g N,N-dimethylacetamide in a three-neck flask; adding 41.65 g(0.1 mol) aromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 h; then adding 25.78 g (0.08 mol)3,3′,4,4′-benzophenonetetracarboxylic dianhydride to the three-neckflask and stirring for 5 hours to obtain a mixed solution; adding 9.93 g(0.04 mol) 4-phenylethynylphthalic anhydride to the mixed solution,stirring and allowing reaction for 3 hours; then adding 60 g toluene,heating to a temperature of 130° C. and carrying out reflux reaction for10 hours under a temperature condition of 130° C. to obtain thepolyimide solution;

the 3,3′,4,4′-benzophenonetetracarboxylic dianhydride has a structuralformula of:

the aromatic diamine has a structural formula of:

the CAS number of the aromatic diamine is: 4402-17-9;

the polyimide in the polyimide solution has a structural formula of:

where Ar₂ has a structural formula of:

Synthesis Embodiment 5

The polyimide solution is prepared according to the following steps:adding 180 g N,N-dimethylacetamide in a three-neck flask; adding 41.65 g(0.1 mol) aromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 h; then adding 29.00 g (0.09 mol)3,3′,4,4′-benzophenonetetracarboxylic dianhydride to the three-neckflask and stirring for 5 hours to obtain a mixed solution; adding 4.96 g(0.02 mol) 4-phenylethynylphthalic anhydride to the mixed solution,stirring and allowing reaction for 3 hours; then adding 60 g toluene,heating to a temperature of 130° C. and carrying out reflux reaction for10 hours under a temperature condition of 130° C. to obtain thepolyimide solution;

the 3,3′,4,4′-benzophenonetetracarboxylic dianhydride has a structuralformula of:

the aromatic diamine has a structural formula of:

the CAS number of the aromatic diamine is: 4402-17-9;

the polyimide in the polyimide solution has a structural formula of:

where Ar₂ has a structural formula of:

Embodiment 1

A polyimide film is manufactured by: 100 parts by weight of polyimidesolution; 20 parts by weight of inorganic filler modifier; and 1 part byweight of interface coupling agent;

the inorganic filler modifier consists of 17 parts by weight of fumedsilica (silicon dioxide in gaseous state) and 3 parts by weight of boronnitride;

the interface coupling agent is γ-aminopropyltriethoxysilane; thepolyimide solution is the polyimide solution of synthesis embodiment 1;

a method of preparing polyimide film comprises the following steps:

(1) weighing to obtain 100 parts of polyimide solution, 20 parts ofinorganic filler modifier and 1 part of interface coupling agent; adding20 parts of inorganic filler modifier and 1 part of interface couplingagent to 100 parts of polyimide solution under a temperature of 90° C.and stirring conditions; and stirring for 30 min to obtain an adhesiveagent;

(2) filtering and degassing the adhesive agent, casting to a rotatingdrum, which is made of stainless steel and loaded with carrier cloth andrelease paper, to obtain a self-supporting film; then under atemperature of 60° C., heating for 60 min, then under a temperature of150° C., heating for 5 min, and finally under a temperature of 60° C.,annealing for 5 min to obtain a polyimide film;

the polyimide film has a thickness of 0.40 mm; the carrier cloth is anE-glass fiberglass cloth having a surface density of 110 g/cm²; theinorganic filler modifier has an average particle size of 5 μm.

Embodiment 2

This embodiment differs from Embodiment 1 in that: the polyimidesolution is the polyimide solution as prepared in synthesis embodiment2. Others are the same as in the Embodiment 1.

Embodiment 3

This embodiment differs from Embodiment 1 in that: the polyimidesolution is the polyimide solution as prepared in synthesis embodiment3. Others are the same as in the Embodiment 1.

Embodiment 4

This embodiment differs from Embodiment 1 in that: the polyimidesolution is the polyimide solution as prepared in synthesis embodiment4. Others are the same as in the Embodiment 1.

Embodiment 5

This embodiment differs from Embodiment 1 in that: the polyimidesolution is the polyimide solution as prepared in synthesis embodiment5. Others are the same as in the Embodiment 1.

Embodiment 6

A polyimide film is manufactured by: 100 parts by weight of polyimidesolution; 3 parts by weight of inorganic filler modifier; and 1 part byweight of interface coupling agent;

the inorganic filler modifier consists of 2 parts by weight of fumedsilica (silicon dioxide in gaseous state) and 1 part by weight of boronnitride;

the interface coupling agent is γ-aminopropyltriethoxysilane;

the polyimide solution is the polyimide solution of synthesis embodiment1;

a method of preparing polyimide film comprises the following steps:

(1) weighing to obtain 100 parts of polyimide solution, 3 parts ofinorganic filler modifier and 1 part of interface coupling agent; adding3 parts of inorganic filler modifier and 1 part of interface couplingagent to 100 parts of polyimide solution under a temperature of 90° C.and stirring conditions; and stirring for 30 min to obtain an adhesiveagent;

(2) filtering and degassing the adhesive agent, casting to a rotatingdrum, which is made of stainless steel and loaded with carrier cloth andrelease paper, to obtain a self-supporting film; then under atemperature of 60° C., heating for 60 min, then under a temperature of150° C., heating for 5 min, and finally under a temperature of 60° C.,annealing for 5 min to obtain a polyimide film;

the polyimide film has a thickness of 0.4 mm; the carrier cloth is anE-glass fiberglass cloth having a surface density of 110 g/cm²; theinorganic filler modifier has an average particle size of 5 μm.

Embodiment 7

This embodiment differs from Embodiment 6 in that: the polyimide film ismanufactured by: 100 parts by weight of polyimide solution; 36 parts byweight of inorganic filler modifier; and 2 parts by weight of interfacecoupling agent; the inorganic filler modifier consists of 30 parts byweight of fused silica (melted silicon dioxide) and 6 parts by weight ofaluminum hydroxide. Others are the same as in the Embodiment 6.

Embodiment 8

This embodiment differs from Embodiment 6 in that: the polyimide film ismanufactured by: 100 parts by weight of polyimide solution; 79 parts byweight of inorganic filler modifier; and 3 parts by weight of interfacecoupling agent; the inorganic filler modifier consists of 70 parts byweight of fused silica (melted silicon dioxide), 3 parts by weight ofaluminum hydroxide, 5 parts by weight of aluminum nitride and 1 part byweight of boron nitride. Others are the same as in the Embodiment 6.

Embodiment 9

This embodiment differs from Embodiment 6 in that: the polyimide film ismanufactured by: 100 parts by weight of polyimide solution; 20 parts byweight of inorganic filler modifier; and 1 part by weight of interfacecoupling agent; the inorganic filler modifier consists of 17 parts byweight of amorphous silica and 3 parts by weight of aluminum oxide.Others are the same as in the Embodiment 6.

Embodiment 10

This embodiment differs from Embodiment 9 in that: the polyimidesolution is the polyimide solution as prepared in synthesis embodiment3. Others are the same as in the Embodiment 9.

Embodiment 11

This embodiment differs from Embodiment 9 in that: the inorganic fillermodifier consists of 17 parts by weight of fumed silica (silicon dioxidein gaseous state) and 3 parts by weight of boron nitride; the polyimidesolution consists of 50 parts by weight of the polyimide solution asprepared in synthesis embodiment 1 and 50 parts by weight of thepolyimide solution as prepared in synthesis embodiment 3. Others are thesame as in the Embodiment 9.

Embodiment 12

This embodiment differs from Embodiment 9 in that: the inorganic fillermodifier consists of 17 parts by weight of fumed silica (silicon dioxidein gaseous state) and 3 parts by weight of boron nitride; the polyimidesolution consists of 50 parts by weight of the polyimide solution asprepared in synthesis embodiment 1 and 50 parts by weight of thepolyimide solution as prepared in synthesis embodiment 4. Others are thesame as in the Embodiment 9.

Embodiment 13

This embodiment differs from Embodiment 9 in that: the inorganic fillermodifier consists of 17 parts by weight of fumed silica (silicon dioxidein gaseous state) and 3 parts by weight of boron nitride; the polyimidesolution consists of 30 parts by weight of the polyimide solution asprepared in synthesis embodiment 1 and 70 parts by weight of thepolyimide solution as prepared in synthesis embodiment 4. Others are thesame as in the Embodiment 9.

Embodiment 14

This embodiment differs from Embodiment 9 in that: the inorganic fillermodifier consists of 17 parts by weight of fumed silica (silicon dioxidein gaseous state) and 3 parts by weight of boron nitride; the polyimidesolution consists of 70 parts by weight of the polyimide solution asprepared in synthesis embodiment 1 and 30 parts by weight of thepolyimide solution as prepared in synthesis embodiment 4. Others are thesame as in the Embodiment 9.

Embodiment 15

filtering and degassing the polyimide solution as prepared in synthesisembodiment 1, casting to a rotating drum, which is made of stainlesssteel and loaded with carrier cloth and release paper, to obtain aself-supporting film; then under a temperature of 60° C., heating for 60min, then under a temperature of 150° C., heating for 5 min, and finallyunder a temperature of 60° C., annealing for 5 min to obtain a polyimidefilm;

the carrier cloth is an E-glass fiberglass cloth having a surfacedensity of 110 g/cm².

Embodiment 16

This embodiment differs from Embodiment 15 in that: the polyimidesolution is the polyimide solution as prepared in synthesis embodiment2. Others are the same as in the Embodiment 15.

Embodiment 17

This embodiment differs from Embodiment 15 in that: the polyimidesolution is the polyimide solution as prepared in synthesis embodiment3. Others are the same as in the Embodiment 15.

Embodiment 18

This embodiment differs from Embodiment 15 in that: the polyimidesolution is the polyimide solution as prepared in synthesis embodiment4. Others are the same as in the Embodiment 15.

Embodiment 19

This embodiment differs from Embodiment 15 in that: the polyimidesolution is the polyimide solution as prepared in synthesis embodiment5. Others are the same as in the Embodiment 15.

Synthesis Embodiment 6

The polyimide solution is prepared according to the following steps:adding 113 g N,N-dimethylacetamide in a three-neck flask; adding 10.8 g(0.1 mol) p-phenylenediamine to the N,N-dimethylacetamide under anitrogen atmosphere and stirring for 1 h; then adding 14.71 g (0.05 mol)3,3′,4,4′-biphenyltetracarboxylic dianhydride to the three-neck flaskand stirring for 5 hours to obtain a mixed solution; adding 24.82 g (0.1mol) 4-phenylethynylphthalic anhydride to the mixed solution, stirringand allowing reaction for 3 hours; then adding 38 g toluene, heating toa temperature of 130° C. and carrying out reflux reaction for 10 hoursunder a temperature condition of 130° C. to obtain the polyimidesolution;

the 3,3′,4,4′-biphenyltetracarboxylic dianhydride has a structuralformula of:

the polyimide in the polyimide solution has a structural formula of:

wherein Ar₂ has a structural formula of:

Synthesis Embodiment 7

The polyimide solution is prepared according to the following steps:adding 113 g N,N-dimethylacetamide in a three-neck flask; adding 10.8 g(0.1 mol) m-phenylenediamine to the N,N-dimethylacetamide under anitrogen atmosphere and stirring for 1 h; then adding 14.71 g (0.05 mol)3,3′,4,4′-biphenyltetracarboxylic dianhydride to the three-neck flaskand stirring for 5 hours to obtain a mixed solution; adding 24.82 g (0.1mol) 4-phenylethynylphthalic anhydride to the mixed solution, stirringand allowing reaction for 3 hours; then adding 37 g toluene, heating toa temperature of 130° C. and carrying out reflux reaction for 10 hoursunder a temperature condition of 130° C. to obtain the polyimidesolution;

the 3,3′,4,4′-biphenyltetracarboxylic dianhydride has a structuralformula of:

the polyimide in the polyimide solution has a structural formula of:

wherein Ar₂ has a structural formula of:

Synthesis Embodiment 8

The polyimide solution is prepared according to the following steps:adding 123 g N,N-dimethylacetamide in a three-neck flask; adding 20.02 g(0.1 mol) 4,4′-diaminodiphenyl ether to the N,N-dimethylacetamide undera nitrogen atmosphere and stirring for 1 h; then adding 25.78 g (0.08mol) 3,3′,4,4′-benzophenonetetracarboxylic dianhydride to the three-neckflask and stirring for 5 hours to obtain a mixed solution; adding 9.93 g(0.04 mol) 4-phenylethynylphthalic anhydride to the mixed solution,stirring and allowing reaction for 3 hours; then adding 41 g toluene,heating to a temperature of 130° C. and carrying out reflux reaction for10 hours under a temperature condition of 130° C. to obtain thepolyimide solution;

the 3,3′,4,4′-benzophenonetetracarboxylic dianhydride has a structuralformula of:

the polyimide in the polyimide solution has a structural formula of:

wherein Ar₂ has a structural formula of:

Synthesis Embodiment 9

The polyimide solution is prepared according to the following steps:adding 174 g N,N-dimethylacetamide in a three-neck flask; adding 41.65 g(0.1 mol) aromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 h; then adding 10.9 g (0.05 mol) ofpyromellitic dianhydride to the three-neck flask and stirring for 5hours to obtain a mixed solution; adding 24.82 g (0.1 mol)4-phenylethynylphthalic anhydride to the mixed solution, stirring andallowing reaction for 3 hours; then adding 58 g toluene, heating to atemperature of 130° C. and carrying out reflux reaction for 10 hoursunder a temperature condition of 130° C. to obtain the polyimidesolution;

the aromatic diamine has a structural formula of:

the CAS number of the aromatic diamine is: 4402-17-9;

the polyimide in the polyimide solution has a structural formula of:

wherein Ar₂ has a structural formula of:

Comparative Experiment 1

(1) weighing to obtain 100 parts of polyimide solution, 20 parts ofinorganic filler modifier and 1 part of interface coupling agent; adding20 parts of inorganic filler modifier and 1 part of interface couplingagent to 100 parts of polyimide solution under a temperature of 90° C.and stirring conditions; and stirring for 30 min to obtain an adhesiveagent;

the inorganic filler modifier consists of 17 parts by weight of fumedsilica (silicon dioxide in gaseous state) and 3 parts by weight of boronnitride; the interface coupling agent is γ-aminopropyltriethoxysilane;the polyimide solution is the polyimide solution of synthesis embodiment6;

(2) filtering and degassing the adhesive agent, casting to a rotatingdrum, which is made of stainless steel and loaded with carrier cloth andrelease paper, to obtain a self-supporting film; then under atemperature of 60° C., heating for 60 min, then under a temperature of150° C., heating for 5 min, and finally under a temperature of 60° C.,annealing for 5 min to obtain a polyimide film;

the carrier cloth is an E-glass fiberglass cloth having a surfacedensity of 110 g/cm²; the inorganic filler modifier has an averageparticle size of 5 μm.

Comparative Experiment 2

This comparative experiment differs from comparative experiment 1 inthat: the polyimide solution is the polyimide solution as prepared insynthesis embodiment 7. Others are the same as in the comparativeexperiment 1.

Comparative Experiment 3

This comparative experiment differs from comparative experiment 1 inthat: the polyimide solution is the polyimide solution as prepared insynthesis embodiment 8. Others are the same as in the comparativeexperiment 1.

Comparative Experiment 4

This comparative experiment differs from comparative experiment 1 inthat: the polyimide solution is the polyimide solution as prepared insynthesis embodiment 9. Others are the same as in the comparativeexperiment 1.

Comparative Experiment 5

filtering and degassing the polyimide solution, casting to a rotatingdrum, which is made of stainless steel and loaded with carrier cloth andrelease paper, to obtain a self-supporting film; then under atemperature of 60° C., heating for 60 min, then under a temperature of150° C., heating for 5 min, and finally under a temperature of 60° C.,annealing for 5 min to obtain a polyimide film;

the polyimide solution is the polyimide solution as prepared insynthesis embodiment 6; the carrier cloth is an E-glass fiberglass clothhaving a surface density of 100 g/cm².

The polyimide solutions prepared in Synthesis Embodiments 1 to 9 aretested for glass transition temperature, thermal stability, rheology andinfrared, results are as shown in Table 1 and FIGS. 1 to 3. The curingprocess of the polyimide solution is as follows: first, heating for 1 hat a temperature of 180° C. and a pressure of 0.2 MPa, and then heatingfor 4 h at a temperature of 350° C. and a pressure of 0.2 MPa.Rheological test: The polyimide solution is introduced into distilledwater, and the precipitate is washed with water and subjected to arheological test after drying.

The test conditions for each test item refer to the following standards(methods):

1. The glass transition temperature is a dynamic thermomechanical (DMA).Heating rate: 5° C./min; frequency: 1 Hz.

2. Thermal stability: The test uses a thermogravimetric analyzer (TGA).Heating rate: 10° C./min; test atmosphere: air.

3. Rheology: using a rotary rheometer, heating rate 4° C./min, testatmosphere: air. Frequency: 1 Hz.

4. The infrared spectrum is measured by Fourier transform infraredspectroscopy by using potassium bromide as the background and the numberof scans is 128.

The polyimide film prepared in Embodiments 1˜19 and ComparativeExperiments 1˜5 is placed between two material items to be bonded, andthe curing process is as follows: first, heating for 1 h at atemperature of 180° C. and a pressure of 0.2 MPa, then heating for 4 hat a temperature of 350° C. and a pressure of 0.2 MPa. Then the bondedmaterial items are tested for shear strength, peel strength and flatwisetensile strength and results are shown in Table 2 and Table 3. The testconditions for each test item refer to the following standards(methods):

1. Shear strength: GB/T7124-2008 Adhesive—Determination of tensilelap-shear strength of rigid-to-rigid bonded assemblies; GJB444-1988Adhesive high temperature shear strength testing. Material: 304stainless steel.

2. Peel strength and flatwise tensile strength test: GJB130.7-1986 Testmethod for climbing drum peel strength of adhesive-bonded aluminumhoneycomb-sandwich structure; GJB130.4-1986 Test method for flatwisetensile strength of adhesive-bonded aluminum honeycomb-sandwichstructure. The honeycomb is made of titanium alloy honeycomb, and theskin panel is made of titanium alloy plate instead of aluminum alloy.

And for the bonding parts (titanium alloy honeycomb and titanium alloyplate bonding) used in the peel strength and the flatwise tensilestrength test, the melt climbing during the curing process is observed,the fillet formation after curing is observed.

FIG. 1 is an infrared spectrum, 1 is an infrared curve after curing ofthe polyimide solution prepared in synthesis embodiment 1; and 2 is aninfrared curve after curing of the polyimide solution prepared insynthesis embodiment 3. From the figure, characteristic absorption peaksof imine, that is asymmetric and symmetrical stretching vibration peaksof carbonyl groups, is observed at both 1780 cm⁻¹ and 1720 cm-1; astretching vibration peak of CN of imide ring and benzimidazole ring isobserved at 1380 cm-1; an absorption peak of C═O is observed at 1660cm-1, showing the presence of dianhydride of benzophenone structure; theN—H bond unique to imidazole is observed in 3000 cm-1˜3500 cm-1; the C≡Ccharacteristic peak at 2200 cm-1 is disappeared after curing at 350° C.,demonstrating that crosslinking is complete.

FIG. 2 is a rheological graph, 1 is a rheological curve of polyimide inthe polyimide solution prepared in synthesis embodiment 1; 2 is arheological curve of polyimide in the polyimide solution prepared insynthesis embodiment 6; and 3 is the rheological curve of polyimide inthe polyimide solution prepared in synthesis embodiment 3. From thefigure, the polyimide solutions prepared in Synthesis embodiments 1 and3 both have a wider processing interval and a lower melt viscosity,ensuring high-temperature meltability and melt climbing ability in thecore structure. On the other hand, since the polyimide solution preparedin Synthesis embodiment 6 does not use a benzimidazole diaminecontaining a flexible carbonyl group, and has a structure withrelatively high rigidity such as p-phenylenediamine, this leads to lackof melt viscosity at high temperature, and hence failure to provideclimbing ability and bonding to the core structure.

Therefore, all of the polyimide solutions synthesized in the synthesisembodiments 1 to 5 have melt fluidity. With the presence of theinorganic filler, the thixotropy and the fillet formation ability isimproved, and a good bonding effect can be obtained.

FIG. 3 is a dynamic thermomechanical curve, 1 is a dynamicthermomechanical curve after curing of the polyimide solution preparedin synthesis embodiment 1; 2 is a dynamic thermomechanical curve aftercuring of the polyimide solution prepared in synthesis embodiment 3; 3is a dynamic thermomechanical curve after curing of the polyimidesolution prepared in synthesis embodiment 5, and 4 is a dynamicthermomechanical curve after curing of the polyimide solution preparedin synthesis embodiment 8. From FIG. 3 and Table 1, 2 and 3, it can beseen that in the synthesis embodiments 1-5, because of the combinationof the benzimidazole ring and the benzoimine ring is used, the Tg isabove 390° C., and when the storage modulus exceeds Tg+30° C., adownward trend of less than 0.5 orders of magnitude can still bemaintained. Therefore, it provides a basis for the high temperatureresistance of 400° C.˜450° C. For examples, the embodiments 1 to 19, asprepared by using the synthesis embodiments 1 to 5, have a relativelygood shear strength at above 400° C. and a relatively good strength at260° C. to 300° C. after aging. On the other hand, in the synthesisembodiment 8, the flexible structure diamine is used to provide meltprocessibility, lower the postcure Tg value, and a decrease in retentionrate of the storage modulus (>2 orders of magnitude), therefore nostrength at high temperature is observed in comparative experiment 3.

In Embodiments 15 to 19 and Comparative Experiment 5, the inorganicfiller modifier is not used, thus resulting in poor surface quality anda high crack depth ratio of the film.

In Embodiments 15 to 19 synthesized by the synthesis embodiments 1˜5,the inorganic filler modifier is not added. In Embodiments 6 synthesizedby the synthesis embodiments 1, a less amount of the inorganic fillermodifier is added. In the above two cases (no or less inorganic fillermodifier), the resin has melt flow and climbing ability but no filletformation at high temperature will occur, thus resulting low coretensile strength and low peel strength. In Embodiments 8 synthesized bythe synthesis embodiments 1, an excessive amount of the inorganic fillermodifier is added, this leads to bonding of the core structure, no meltclimbing ability of the resin and no fillet formation at hightemperature, thus also decreasing the plane tensile strength of the corestructure and roller peel strength. In Embodiments 6˜9 synthesized bythe synthesis embodiments 1˜5, the comparative embodiment 1, 2, 4 and 5do not have resin melt fluidity, resulting low plane tensile strengthand peel strength of the core structure; the comparative 3 does haveresin melt fluidity but does not use a combination of Benzimidazole ringand benzoimine ring, thus resulting low Tg and low shear strength athigh temperature.

TABLE 1 Properties comparison table of synthesis embodiment synthesissynthesis synthesis synthesis synthesis synthesis synthesis synthesissynthesis embodi- embodi- embodi- embodi- embodi- embodi- embodi-embodi- embodi- ment 1 ment 2 ment 3 ment 4 ment 5 ment 6 ment 7 ment 8ment 9 Glass Transition 465 440 445 412 398 480 475 298 473 Temp/° C.Initial thermo- 580 585 575 572 570 590 586 559 585 gravimetric temp/°C.

TABLE 2 Properties comparison table of embodiment 1 to 11 Embodiment 1Embodiment 2 Embodiment 3 Embodiment 4 Embodiment5 Embodiment 6 FilmQuality Good Good Good Good Good Good Shear 25° C. 24 28 27 30 32 26Strength/ 300° C. 23 23 24 21 20 23 MPa 400° C. 15 11 12 9 9 14 450° C.13 7 10 6 4 12 500° C. 8 4 7 3 2 8 Roller Peel 25° C. 74.4 89.3 85.398.3 116.6 28.2 Strength 300° C. 79.2 87.3 93.6 99.3 96.1 20.4 (N · m/m)Planar Tensile Strength/MPa 3.7 4.2 3.9 4.1 4.2 1.2 Melt Climbing GoodGood Good Good Good Good Fillet Formation Good Good Good Good Good NoFillet Formed Shear strength/MPa at room 25 29 28 30 31 25 temperatureafter heat aging at 260° C. for 500 h Shear strength/MPa at room 24 2826 27 28 22 temperature after heat aging at 300° C. for 500 h Embodiment7 Embodiment 8 Embodiment 9 Embodiment 10 Embodiment 11 Film QualityGood Good Good Good Good Shear 25° C. 20 17 23 27 25 Strength/ 300° C.20 19 24 23 23 MPa 400° C. 15 13 14 12 14 450° C. 13 13 13 9 11 500° C.9 8 8 7 8 Roller Peel 25° C. 43.2 <10 72.1 73.1 80.3 Strength 300° C.40.2 <10 74.3 76.3 83.2 (N · m/m) Planar Tensile Strength/MPa 2.7 / 3.63.7 3.9 Melt Climbing Ordinary No Climbing Good Good Good FilletFormation Ordinary No Fillet Good Good Good Formed Shear strength/MPa atroom 21 18 21 26 24 temperature after heat aging at 260° C. for 500 hShear strength/MPa at room 20 16 19 25 22 temperature after heat agingat 300° C. for 500 h

TABLE 3 Properties comparison table of embodiment 12 to 19 andcomparative experiment 1 to 5 Embodi- Embodi- Embodi- Embodi- Embodi-Embodi- Embodi- ment 12 ment 13 ment 14 ment 15 ment 16 ment 17 ment 18Film Quality Good Good Good Poor surface Poor surface Poor surface Poorsurface flatness flatness flatness flatness Shear 25° C. 27 28 25 26 2828 31 Strength/ 300° C. 22 22 23 24 23 24 22 MPa 400° C. 11 10 13 15 1111 9 450° C. 9 7 12 12 6 10 6 500° C. 6 4 7 8 4 6 3 Roller Peel 25° C.90.2 93.2 82.3 24.0 30.2 27.2 30.2 Strength 300° C. 91.2 94.3 85.3 28.229.4 28.2 31.2 (N · m/m) Planar Tensile Strength/MPa 4.0 4.1 3.9 1.1 1.11.2 1.2 Melt Climbing Good Good Good Good Good Good Good FilletFormation Good Good Good No fillet No fillet No fillet No fillet Shearstrength/MPa at room 27 27 24 26 25 24 28 temperature after heat agingat 260° C. for 500 h Shear strength/MPa at room 25 25 23 25 20 20 23temperature after heat aging at 300° C. for 500 h Embodi- ComparativeComparative Comparative Comparative Comparative ment 19 experiment 1experiment 2 experiment 3 experiment 4 experiment 5 Film Quality Poorsurface Good Good Good Good Poor surface flatness flatness Shear 25° C.35 19 20 28 20 20 Strength/ 300° C. 21 17 17 13 19 17 MPa 400° C. 9 1010 4 15 9 450° C. 3 8 7 0 11 8 500° C. 2 6 5 0 7 5 Roller Peel 25° C.33.2 <10 <10 17.2 <10 <10 Strength 300° C. 31.2 <10 <10 13.2 <10 <10 (N· m/m) Planar Tensile Strength/MPa 1.2 / / 0.3 / / Melt Climbing Good Noclimbing No climbing Good No climbing No climbing Fillet Formation Nofillet No fillet No fillet No fillet No fillet No fillet Shearstrength/MPa at room 31 18 19 21 19 27 temperature after heat aging at260° C. for 500 h Shear strength/MPa at room 28 16 17 17 15 14temperature after heat aging at 300° C. for 500 h

What is claimed is:
 1. A high temperature resistant polyimide film,characterized in that: the polyimide film is manufactured by: 100 partsby weight of polyimide solution; 10 parts to 40 parts by weight ofinorganic filler modifier; and 0.1 parts˜5 parts by weight of interfacecoupling agent, wherein the inorganic filler modifier consists ofsilicon dioxide (silica)-based substance and substance for increasinginterface bonding, and the mass ratio of the silica-based substance andthe substance for increasing interface bonding is 1:(0.1˜0.5), thesilica-based substance is hollow ceramic microspheres, fumed silica(silicon dioxide in gaseous state), fused silica (melted silicondioxide) or amorphous silica, the substance for increasing interfacebonding is one or a mixture of two or more selected from the groupconsisting of: aluminum hydroxide, magnesium hydroxide, molybdenumoxide, aluminum nitride, aluminum oxide, boron nitride and siliconcarbide, the polyimide solution comprises polyimide which has astructural formula of:

where n is 1˜19; wherein A₁ has a structural formula of:

wherein Ar₂ has a structural formula of:


2. The high temperature resistant polyimide film according to claim 1,characterized in that: the polyimide solution is manufactured by aprocess comprising the steps of: adding N,N-dimethylacetamide, addingaromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 hour to 5 hours, then adding aromaticdianhydride and stirring for 1 hour to 5 hours to obtain a mixedsolution, adding 4-phenylethynylphthalic anhydride to the mixed solutionand stirring and allowing reaction for 1 hour to 5 hours, then addingtoluene, heating to a temperature of 120° C.˜130° C., and carrying outreflux reaction for 5˜20 hours under a temperature condition of 120°C.˜130° C. to obtain the polyimide solution, wherein a molar ratio ofaromatic dianhydride to aromatic diamine is (0.50˜0.95):1; a mass ratioof N,N-dimethylacetamide to toluene is 1:(0.2˜0.5); a molar ratio ofaromatic diamine to 4-phenylethynylphthalic anhydride is 1:(0.01-1); anda total number of moles of anhydride functional group in the aromaticdianhydride and 4-phenylethynyl phthalic anhydride is equal to thenumber of moles of amino functional group of the aromatic diamine; atotal mass ratio of the N,N-dimethylacetamide and the toluene to a totalmass ratio of the 4-phenylethynylphthalic anhydride, the aromaticdianhydride and the aromatic diamine is (2.5˜4):1; the aromaticanhydride is selected from the group consisting of:

the aromatic diamine has a structural formula of:

where R₁ is O or NH.
 3. The high temperature resistant polyimide filmaccording to claim 1, characterized in that: the inorganic fillermodifier has an average particle diameter of 0.1 μm to 10 μm; theinterface coupling agent is a silane coupling agent containing amino endgroup.
 4. The high temperature resistant polyimide film according toclaim 3, characterized in that: the silane coupling agent containingamino end group is selected from the group consisting of:γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane and3-aminopropylmethyldiethoxysilane.
 5. A method of preparing hightemperature resistant polyimide film, characterized in that: the methodof preparing high temperature resistant polyimide film comprises thesteps of: (a) weighing to obtain 100 parts of polyimide solution, 10parts to 40 parts of inorganic filler modifier and 0.1 part to 5 partsof interface coupling agent; adding 10 to 40 parts of inorganic fillermodifier and 0.1 part to 5 parts of interface coupling agent to 100parts of polyimide solution under a temperature of 90° C. to 120° C. andstirring conditions; and stirring for 10 minutes to 30 minutes to obtainan adhesive agent; wherein the polyimide solution is manufactured by aprocess comprising the steps of: adding N,N-dimethylacetamide; addingaromatic diamine to the N,N-dimethylacetamide under a nitrogenatmosphere and stirring for 1 hour to 5 hours; then adding aromaticdianhydride and stirring for 1 hour to 5 hours to obtain a mixedsolution; adding 4-phenylethynylphthalic anhydride to the mixedsolution, stirring and allowing reaction for 1 hour to 5 hours; thenadding toluene, heating to a temperature of 120° C. to 130° C. andcarrying out reflux reaction for 5 hours to 20 hours under a temperaturecondition of 120° C.˜130° C. to obtain the polyimide solution; wherein amolar ratio of aromatic dianhydride to aromatic diamine is(0.50˜0.95):1; a mass ratio of N,N-dimethylacetamide to toluene is1:(0.2˜0.5); a molar ratio of aromatic diamine to4-phenylethynylphthalic anhydride is 1:(0.01˜1); and a total number ofmoles of anhydride functional group in the aromatic dianhydride and4-phenylethynyl phthalic anhydride is equal to the number of moles ofamino functional group of the aromatic diamine; a ratio of a total massof the N,N-dimethylacetamide and the toluene to a total mass of the4-phenylethynylphthalic anhydride, the aromatic dianhydride and thearomatic diamine is (2.5˜4):1; the aromatic anhydride is selected fromthe group consisting of:

the aromatic diamine has a structural formula of:

where R₁ is O or NH; (b) filtering and degassing the adhesive agent,casting to a drum made of stainless steel and loaded with carrier clothand release paper to obtain a self-supporting film; then under atemperature of 60° C. to 150° C., heating for 1 min to 60 min, thenunder a temperature of 150° C. to 300° C., heating for 1 min to 60 min,and finally under a temperature of 50° C. to 140° C., annealing for 1min to 20 min to obtain high temperature resistant polyimide film;wherein the high temperature resistant polyimide film has a thickness of0.30 mm˜0.60 mm; in the step (a), the inorganic filler modifier consistsof silicon dioxide (silica)-based substance and substance for increasinginterface bonding, and the mass ratio of the silica-based substance andthe substance for increasing interface bonding is 1:(0.1˜0.5), thesilica-based substance is hollow ceramic microspheres, fumed silica(silicon dioxide in gaseous state), fused silica (melted silicondioxide) or amorphous silica, the substance for increasing interfacebonding is one or a mixture of two or more selected from the groupconsisting of: aluminum hydroxide, magnesium hydroxide, molybdenumoxide, aluminum nitride, aluminum oxide, boron nitride and siliconcarbide, in the step (a), the polyimide solution comprises polyimidewhich has a structural formula of:

where n is 1˜19; where Ar₁ has a structural formula of:

where Ar₂ has a structural formula of:

where R₁ is O or NH.
 6. The method of preparing high temperatureresistant polyimide film according to claim 5, characterized in that: inthe step (a), the inorganic filler modifier has an average particlediameter of 0.1 μm to 10 μm.
 7. The method of preparing high temperatureresistant polyimide film according to claim 5, characterized in that: inthe step (a), the interface coupling agent is a silane coupling agentcontaining amino end group.
 8. The method of preparing high temperatureresistant polyimide film according to claim 7, characterized in that:the silane coupling agent containing amino end group is selected fromthe group consisting of: γ-aminopropyltriethoxysilane,3-aminopropyltrimethoxysilane and 3-aminopropylmethyldiethoxysilane. 9.The method of preparing high temperature resistant polyimide filmaccording to claim 5, characterized in that: in the step (b), thecarrier cloth is selected from the group consisting of: E-glassfiberglass cloth, D-glass fiberglass cloth, S-glass fiberglass cloth,NE-glass fiberglass cloth, T-glass fiberglass cloth and Q-glassfiberglass cloth.
 10. The method of preparing high temperature resistantpolyimide film according to claim 9, characterized in that: the carriercloth has a surface density of 100 g/cm²˜110 g/cm².